Can fully iterative reconstruction technique enable routine abdominal CT at less than 1 mSv?

Abstract

Objective We assessed the effect of the forward projected model-based reconstruction technique (FIRST) on lesion detection of routine abdomen CT at <1 mSv. Materials and methods Thirty-seven adult patients gave written informed consent for acquisition of low-dose CT (LDCT) immediately after their clinically-indicated, standard of care dose (SDCT), routine abdomen CT on a 640-slice MDCT (Aquillion One, Canon Medical System). The LDCT series were reconstructed with FIRST (at STD (Standard) and STR (Strong) levels), and SDCT series with filtered back projection (FBP). Two radiologists assessed lesions in LD-FBP and FIRST images followed by SDCT images. Then, SDCT and LDCT were compared for presence of artifacts in a randomized and blinded fashion. Patient demographics, size and radiation dose descriptors (CTDIvol, DLP) were recorded. Descriptive statistics and inter-observer variability were calculated for data analysis. Results Mean CTDIvol for SDCT and LDCT were 13 ± 4.7 mGy and 2.2 ± 0.8 mGy, respectively. There were 46 true positive lesions detected on SDCT. Radiologists detected 38/46 lesions on LD-FIRST-STD compared to 26/46 lesions on LD-FIRST-STR. The eight lesions (liver and kidney cysts, pancreatic lesions, sub-cm peritoneal lymph node) missed on LD-FIRST-STD were seen in patients with BMI > 25.8 kg/m 2 . Diagnostic confidence for lesion assessment was optimal in LD-FIRST-STD setting in most patients regardless of their size. The inter-observer agreement (kappa-value) for overall image quality were 0.98 and 0.84 for LD-FIRST-STD and STR levels, respectively. Conclusion FIRST enabled optimal lesion detection in routine abdomen CT at less than 1 mSv radiation dose in patients with body mass less than ≤25.8 kg/m 2 .

Low-dose CT for diagnosing intestinal obstruction and pneumoperitoneum; need for retakes and diagnostic accuracy

“…5,6,17 The reason for this discrepancy is probably that our LD-CT protocol did not include iterative reconstruction, which has the potential to lower radiation dose substantially. 18 The low number of patients diagnosed with paralytic ileus in our study is possibly in part due to the high number of CT scans registered as possible intestinal obstruction, where a transition zone was not identified. Additionally, most patients presenting with paralytic ileus at our institution are in the post-operative period.…”

“…5,6,17 The reason for this discrepancy is probably that our LD-CT protocol did not include iterative reconstruction, which has the potential to lower radiation dose substantially. 18…”

Image quality evaluation of dual-layer spectral CT in comparison to single-layer CT in a reduced-dose setting

“…These differences did not lead to significant differences in subjective image quality, as delineation of vasculature is but one aspect of overall image quality. While Singh et al or Tabari et al [22,28] suggest to link the evaluation of image quality to the clinical task of lesion detection, this approach was not applicable to this study as not all patients had lesions in all three evaluated body regions. In consequence, future studies may evaluate different aspects of image quality to provide a more complete evaluation for different clinical tasks.…”

Can optimized model-based iterative reconstruction improve the contrast of liver lesions in CT?

“…There has been limited testing of the use of FIRST algorithms in abdominal imaging so far. Tabari et al showed the possibility of using FIRST reconstruction for sub-Millisievert imaging, showing significant increases in SNR and CNR of abdominal lesions in comparison to FBP in sub-Millisievert CT imaging (27). Our study only evaluated lesions in a standard imaging protocol, without additional analysis of ultra-low-dose imaging.…”